When three siblings decided to sell a sculpture signed by a famous artist, they were told that it was a copy worth about $1,500 -- so it's a good thing they sought a second opinion.

That piece of art, it turns out, really was cast by renowned French sculptor Auguste Rodin. A Falls Church, Virginia, auctioneer thinks it could fetch about $135,000 when it goes up for sale this weekend.

"Le Desespoir" once belonged to the grandfather of three siblings -- including two sisters who live in the D.C. area -- who'd grown up believing it was the real thing.

Elizabeth Tillson of McLean, Virginia, said her parents had three appraisals that said it was real, so they were startled when a New York auction house told them it was just a copy.

"We were very disappointed," she said. Unsure of what to do, they brought it home from New York and kept it at home while doing some soul-searching. Eventually, they contacted Matt Quinn of Quinn's Auction Gallery in Falls Church.

Quinn wasn't so sure that the New York auction house was right.

"It sat on the floor in the office for awhile," he said, "and I kept looking at it, and I was like, 'ahh, there's something about it,' and I wasn't so convinced that this piece wasn't at least 100 years old...."

Eventually, Quinn's uncle suggested they remove the sculpture from its base. When they did, they discovered a second "A. Rodin" signature in raised lettering, a style that was difficult to do and unusual at the time. They did some further research and then contacted Rodin experts who deemed the sculpture to be authentic.

It was exciting news to Tillson and her siblings, Ann Farquhar of Bethesda, Maryland, and Tim Mathiasen of Pennington, New Jersey. Tillson said they'd always felt it was real, and their grandfather, who died in the 1960s, had owned other valuable pieces.

The siblings have traded off the sculpture over the years, but they've decided to let it go and split the proceeds. They've saved other things from the family that are meaningful to them, Tillson said.

"We... had already taken pieces that we knew were very special to our parents," she said.

Published at 10:22 PM CDT on May 15, 2014 | Updated at 3:00 PM CDT on May 18, 2014